Effect of Four Triazine Herbicides on Growth of Nontarget Green Algae

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Abstract
Colorimetry, nephelometry, and chlorophyll assays of cultures ofChlamydomonas reinhardtiiDangeard,Chlorella pyrenoidosaChick., andScenedesmus quadricauda(Turp.) Bréb. were used as criteria for measuring algae growth. Among the fours-triazines studied, cyprazine appeared to be the most inhibitory to algae growth, followed by atrazine > simazine > cyanazine. Stimulatory effects of cyanazine, simazine, and cyprazine on chlorophyll content ofC. reinhardtiiandC. pyrenoidosawere also observed. Cyanazine was most stimulatory on both species but simazine also showed stimulation. Cyprazine was stimulatory only toC. reinhardtiiat 0.22 μM concentration but apparently was inhibitory toC. pyrenoidosaat the same concentration. In one experiment, atrazine caused a slight stimulation inC. reinhardtii. Averaged over two consecutive experiments, however, atrazine was inhibitory. Chlorophyll content of the algae was found to be the best criterion for determining effect of the chemicals on algae growth. Continuous exposure ofC. reinhardtiiculture to the highest concentration of each of the four herbicides resulted in selection of algal lines having increased triazine tolerance.